Curable polyphenylene ether-polyepoxide compositions useful in printed circuit board production

ABSTRACT

Curable compositions containing a reaction product of at least one bisphenol polyglycidyl ether, at least one epoxidized novolak and at least one brominated bisphenol, in combination with a polyphenylene ether and further components including specific catalysts and hardeners, may be used in the preparation of laminates useful as printed circuit boards and having excellent physical and electrical properties.

This invention relates to resinous compositions useful as dielectrics,and more particularly to polyphenylene ether-polyepoxide compositionssuitable for fabrication into printed circuit boards.

A number of polyphenylene ether-polyepoxide compositions havingfavorable dielectric properties, and supposedly being useful in circuitboard manufacture, are known. However, for the most part these have notattained wide commercial use because of deficiencies in one or moreproperties. Thus, while the polyphenylene ethers are excellentdielectrics and the properties of combinations thereof with polyepoxidesare favorable in this respect, they lack solvent resistance which isrequired in order for the circit board to survive cleaning with suchsolvents as methylene chloride. Other deficiencies are found in areassuch as flammability, solderability and resistance to high temperatures.Moreover, times required for curing such compositions are typically toolong for effective manufacture of circuit boards in large volume.

In addition to excellent dielectric properties, resinous compositions tobe used for printed circuit board manufacture should be highlyflame-retardant. A V-1 rating, as determined by UnderwritersLaboratories test procedure UL-94, is universally required with V-0usually being necessary. The V-0 rating requires a flame-out time (FOT)of not more than 10 seconds in any trial and a cumulative FOT of notmore than 50 seconds for five samples. As a practical matter, a maximumcumulative FOT of 35 seconds is often mandated by purchasers.

The fabricated board should not lose substantial weight and its surfaceshould not be appreciably marred by contact with methylene chloride.Solderability should be good, as evidenced by the lowest possiblepercent increase in thickness (Z-axis expansion) of the board whenexposed to liquid solder at 288° C. In addition to all these propertiesof the cured material, a relatively short curing time is highlydesirable.

Copending, commonly owned application Ser. No. 92,725, filed Sept. 3,1987 (Now abandoned and a parent of application Ser. No. 07/287,604)discloses polyphenylene ether-polyepoxide composition which are curableby a zinc or aluminum salt of a diketone such as acetylacetone,optionally in the presence of a phenolic compound or basic nitrogencompound as a curing accelerator. While these compositions haveexcellent dielectric properties and solder and solvent resistance, thereis room for improvement in flame retardancy and curing time.

In Japanese Kokai No. 58/69052, combinations of polyphenylene etherswith various types of polyepoxides are disclosed. The latter includeepoxy novolak resins and polyglycidyl ethers of such compounds asbisphenol A and 3,5,3',5'-tetrabromobisphenol A. Curing of thesecompositions is achieved by contact with various known curing agents,including amines. The cured compositions, however, have been found to beseriously deficient in solvent resistance and, in certain cases, insolderability.

The present invention provides a series of resinous compositions whichcomprise polyepoxides, polyphenylene ethers and various catalysts,hardeners, flame retardants and other constituents. When used toimpregnate suitable fibrous reinforcing materials such as glass fibercloth, they furnish workable prepregs. Said compositions are readilysoluble in organic solvents, facilitating impregnation. The curedmaterials prepared therefrom are highly solder resistant, solventresistant and flame retardant, and have excellent dielectric propertiesand dimensional stability at high temperatures. Therefore, said curedmaterials are excellent when employed as laminates for printed circuitboards.

In one of its aspects, the invention includes curable compositionscontaining chemically combined bromine in an amount effective to impartflame retardancy and comprising:

(I) about 25-50% of a resinous composition containing 15-20% chemicallycombined bromine and comprising the reaction product obtained byheating, in the presence of a catalytic amount of at least one basicreagent, a mixture comprising:

(A) at least one halogen-free bisphenol polyglycidyl ether having anaverage of at most one aliphatic hydroxy group per molecule;

(B) about 15-25% of at least one halogen-free epoxidized novolak; and

(C) 25-35% of at lest one bisphenol containing bromine as arylsubstituents;

the percentages of components B and C being based on total reagents A, Band C;

(II) about 35-55% of at least one polyphenylene ether;

(III) about 4-15% of at least one halogen-free novolak, substantiallyall oxygen therein being in the form of phenolic hydroxy groups;

(IV) an amount of at least one of imidazoles and arylene polyamines toprovide a total of at least 4.5 milliequivalents of basic nitrogen per100 parts of said curable composition;

(V) about 0.1-1.0% of zinc in the form of a zinc salt which is solubleor stably dispersible in said curable composition; and

(VI) about 1-4% of antimony pentoxide stably dispersed in said curablecomposition;

said composition being dissolved in an effective amount of an inertorganic solvent;

said percentages being by weight and based on the total of componentsI-VI and any other resinous materials and brominated materials present.

Component I in the compositions of this invention is prepared by thereaction of two or three reagents of which reagent A is at least onehalogen-free bisphenol polyglycidyl ether. The most common compounds ofthis type are prepared by the reaction of bisphenols withepichlorohydrin. (By "bisphenol" as used herein is meant a compoundcontaining two hydroxyphenyl groups attached to an aliphatic orcycloaliphatic moiety, which may also contain aromatic substituents.)Said compounds may be represented by the formula ##STR1## wherein n hasan average value up to 1, each of A¹ and A² is a monocyclic divalentaromatic radical and Y is a bridging radical in which one or two atomsseparate A¹ from A². The O-A¹ and A² -bonds in formula I are usually inthe meta or para positions of A¹ and A² in relation to Y.

In formula I, the A¹ and A² values may be unsubstituted phenylene orsubstituted derivatives thereof, illustrative substituents (one or more)being alkyl, nitro, alkoxy and the like. Unsubstituted phenyleneradicals are preferred. Each of A¹ and A² may for example. be o- orm-phenylene and the other p-phenylene but both are preferablyp-phenylene.

The bridging radical, Y, is one in which one or two atoms, preferablyone, separate A¹ from A². It is most often a hydrocarbon radical andparticularly a saturated radical such as methylene, cyclohexylmethylene,ethylene, isopropylidene, neopentylidene, cyclohexylidene orcyclopentadecylidene, especially a gem-alkylene (alkylidene) radical andmost preferably isopropylidene. Also included, however, are radicalswhich contain atoms other than carbon and hydrogen; for example,carbonyl, oxy, thio, sulfoxy and sulfone.

The materials which are preferred as reagent A are commerciallyavailable reaction products of epichlorohydrin and2,2-bis(4-hydroxyphenyl)propane (bisphenol A), including EPON 825 (n=0)and EPON 828 (n=about 0.14), available from Shell Chemical Co.

Reagent B is at least one halogen-free epoxidized novolak. Suitablenovolaks for use as precursors therefor are known in the art and aretypically prepared by the reaction of formaldehyde with ahydroxyaromatic compound such as phenol (which is often preferred),cresol or t-butylphenol. The novolak then undergoes reaction with anepoxy reagent such as epichlorohydrin to produce the resin useful asreagent B.

Various epoxidized novolaks are commercially available, and any of themmay be used according to the invention. It is usually strongly preferredthat the epoxidized novolak contain substantially no free phenolichydrogen atoms.

Reagent C is at least one bisphenol containing bromine in the form ofsubstituents or the aromatic rings, usually a brominated derivative ofbisphenol A. Its purpose according to the invention is principally toprovide flame retardancy. 2,2-Bis(3,5-dibromo-4-hydroxyphenyl)propane ispreferred as reagent C because of its availability, relatively low costand particular suitability for the purposes of the invention.

As previously mentioned, reagent B comprises about 15-25% and reagent C25-35% of the composition comprising component I, with the balance beingreagent A. Lower concentrations of reagent B or reagent C cause anunacceptable decrease in solvent resistance and/or flame resistance. Anincrease in reagent C may yield an incompatible material. The preferredproportion of reagent C is in the range of 28-32%.

The mixture comprising reagents A, B and C is heated, most often at atemperature in the range of about 125°-225° C., preferably about150°-200° C. and most preferably about 160°-190° C., in the presence ofa catalytic amount of at least one basic reagent. Said mixturepreferably consists essentially of said reagents; that is, they are theonly ones contributing to the novel and essential properties thereof.

The triarylphosphines, especially triphenylphosphine, are the preferredbasic reagents by reason of their effectiveness at low levels, lowtendency to cause side reactions and harmlessness when they remainpresent after the reaction is complete. The proportion of catalyst istypically about 0.1-0.5% by weight. The reaction is preferably conductedin an inert atmosphere such as nitrogen, especially when atriarylphosphine is employed as catalyst. An inert organic solventhaving a boiling point no higher than about 125° C., usually an aromatichydrocarbon such as toluene, may be employed but usually provides noadvantage at this point.

The structure of the resinous composition thus obtained is not fullyknown. It is believed to be an "upstaged" (i.e., partially cured)composition derived from the compounds of formula I, in which thebrominated moieties form part of the molecular structure. The epoxidizednovolak may also be chemically bound into the molecules of the upstagedcomposition in varying proportions.

The preparation of the upstaged compositions is illustrated by thefollowing example.

EXAMPLE 1

A mixture of 50 parts by weight of bisphenol A diglycidyl ether, 30parts of 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 20 parts of anepoxy novolak resin commercially available from Ciba-Geigy under thegrade designation "EPN 1138" and 0.2 part of triphenylphosphine washeated at 165° C. for one hour in a nitrogen atmosphere, with stirring.The product was the desired upstaged composition and contained 17.6%bromine.

For the preparation of curable compositions useful in the manufacture ofprinted circuit boards having the desired properties, component I iscombined with the other materials enumerated above. In particular,intermediates which may be employed in the preparation of suchcompositions include resinous blends containing 5-10% chemicallycombined bromine and comprising about 35-60% of component I and about40-65% of component II, said percentages being by weight of totalresinous components. These resinous blends and the above-describedupstaged compositions are disclosed and claimed in copending, commonlyowned application Ser. No. [RD-18473].

The polyphenylene ethers useful as component II comprise a plurality ofstructural units having the formula ##STR2## In each of said unitsindependently, each Q¹ is independently halogen, primary or secondarylower alkyl (i.e., alkyl containing up to 7 carbon atoms), phenyl,haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein atleast two carbon atoms separate the halogen and oxygen atoms; and eachQ² is independently hydrogen, halogen, primary or secondary lower alkyl,phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined forQ¹. Examples of suitable primary lower alkyl groups are methyl, ethyl,n-propyl, n-butyl, isobutyl, n-amyl, isoamyl, 2-methylbutyl, n-hexyl,2,3-dimethylbutyl, 2-, 3- or 4-methylpentyl and the corresponding heptylgroups. Examples of secondary lower alkyl groups are isopropyl,sec-butyl and 3-pentyl. Preferably, any alkyl radicals are straightchain rather than branched. Most often, each Q¹ is alkyl or phenyl,especially C₁₋₄ alkyl, and each Q² is hydrogen. Suitable polyphenyleneethers are disclosed in a large number of patents.

Both homopolymer and copolymer polyphenylene ethers are included.Suitable homopolymers are those containing, for example,2,6-dimethyl-1,4-phenylene ether units. Suitable copolymers includerandom copolymers containing such units in combination with (forexample) 2,3,6-trimethyl- 1,4-phenylene ether units. Many suitablerandom copolymers, as well as homopolymers, are disclosed in the patentliterature.

Also included are polyphenylene ethers containing moieties which modifyproperties such as molecular weight, melt viscosity and/or impactstrength. Such polymers are described in the patent literature and maybe prepared by grafting onto the polyphenylene ether in known mannersuch non-hydroxy-containing vinyl monomers as acrylonitrile andvinylaromatic compounds (e.g., styrene), or such non-hydroxy-containingpolymers as polystyrenes and elastomers. The product typically containsboth grafted and ungrafted moieties. Other suitable polymers are thecoupled polyphenylene ethers in which the coupling agent is reacted inknown manner with the hydroxy groups of two polyphenylene ether chainsto produce a higher molecular weight polymer containing the reactionproduct of the hydroxy groups and the coupling agent. Illustrativecoupling agents are low molecular weight polycarbonates, quinones,heterocycles and formals.

For the purposes of this invention, the polyphenylene ether has a numberaverage molecular weight within the range of about 3,000-40,000,preferably at least about 12,000 and most preferably at least about15,000, and a weight average molecular weight within the range of about20,000-80,000, as determined by gel permeation chromatography. Itsintrinsic viscosity is most often in the range of about 0.35-0.6 dl./g.,as measured in chloroform at 25° C.

The polyphenylene ethers are typically prepared by the oxidativecoupling of at least one corresponding monohydroxyaromatic compound.Particularly useful and readily available monohydroxyaromatic compoundsare 2,6-xylenol (wherein each Q¹ is methyl and each Q² is hydrogen),whereupon the polymer may be characterized as apoly(2,6-dimethyl-1,4-phenylene ether), and 2,3,6-trimethylphenol(wherein each Q¹ and one Q² is methyl and the other Q² is hydrogen).

A variety of catalyst systems are known for the preparation ofpolyphenylene ethers by oxidative coupling. There is no particularlimitation as to catalyst choice and any of the known catalysts can beused. For the most part, they contain at least one heavy metal compoundsuch as a copper, manganese or cobalt compound, usually in combinationwith various other materials.

A first class of preferred catalyst systems consists of those containinga copper compound. Such catalysts are disclosed, for example, in U.S.Pat. Nos. 3,306,874, 3,306,875, 3,914,266 and 4,028,341. They areusually combinations of cuprous or cupric ions, halide (i.e., chloride,bromide or iodide) ions and at least one amine.

Catalyst systems containing manganese compounds constitute a secondpreferred class. They are generally alkaline systems in which divalentmanganese is combined with such anions as halide, alkoxide or phenoxide.Most often, the manganese is present as a complex with one or morecomplexing and/or chelating agents such as dialkylamines, alkanolamines,alkylenediamines, o-hydroxyaromatic aldehydes, o-hydroxyazo compounds,ω-hydroxyoximes (monomeric and polymeric), o-hydroxyaryl oximes andβ-diketones. Also useful are known cobalt-containing catalyst systems.Suitable manganese and cobalt-containing catalyst systems forpolyphenylene ether preparation are known in the art by reason ofdisclosure in numerous patents and publications.

Particularly useful polyphenylene ethers for the purposes of thisinvention are those which comprise molecules having at least one of theend groups of the formulas ##STR3## wherein Q¹ and Q² are as previouslydefined; each R¹ is independently hydrogen or alkyl, with the provisothat the total number of carbon atoms in both R¹ radicals is 6 or less;and each R² is independently hydrogen or a C₁₋₆ primary alkyl radical.Preferably, each R¹ is hydrogen and each R² is alkyl, especially methylor n-butyl.

Polymers containing the aminoalkyl-substituted end groups of formula IIImay be obtained by incorporating an appropriate primary or secondarymonoamine as one of the constituents of the oxidative coupling reactionmixture, especially when a copper- or manganese-containing catalyst isused. Such amines, especially the dialkylamines and preferablydi-n-butylamine and dimethylamine, frequently become chemically bound tothe polyphenylene ether, most often by replacing one of the α-hydrogenatoms on one or more Q¹ radicals. The principal site of reaction is theQ¹ radical adjacent to the hydroxy group on the terminal unit of thepolymer chain. During further processing and/or blending, theaminoalkyl-substituted end groups may undergo various reactions,probably involving a quninone methide-type intermeidate of the formula##STR4## with numerous beneficial effects often including an increase inimpact strength and compatibilization with other blend components.Reference is made to U.S. Pat. Nos. 4,054,553, 4,092,294, 4,477,649,4,477,651 and 4,517,341, the disclosures of which are incorporated byreference herein.

Polymers with 4-hydroxybiphenyl end groups of formula IV are typicallyobtained form reaction mixtures in which a by-product diphenoquinone ofthe formula ##STR5## is present, especially in a copper-halide-secondaryor tertiary amine system. In this regard, the disclosure of U.S. Pat.No. 4,477,649 is again pertinent as are those of U.S. Pat. Nos.4,234,706 and 4,482,697, which are also incorporated by referenceherein. In mixtures of this type, the diphenonquinone is ultimatelyincorporated into the polymer in substantial proportions, largely as anend group.

In many polyphenylene ethers obtained under the above-describedconditions, a substantial proportion of the polymer molecules, typicallyconstituting as much as about 90% by weight of the polymer, contain endgroups having one or frequently both of formulas III and IV. It shouldbe understood, however, that other end groups may be present and thatthe invention in its broadest sense may not be dependent on themolecular structures of the polyphenylene ether end groups.

It will be apparent to those skilled in the art from the foregoing thatthe polyphenylene ethers contemplated for use in the present inventioninclude all those presently known, irrespective of variations instructural units or ancillary chemical features.

In addition to the polyphenylene ether and the upstaged composition, thecurable compositions of this invention and the above-described resinousblends preferably contain (VII) at least one polyepoxy compound selectedfrom those described hereinabove with reference to reagents A and B.Said polyepoxy compound acts to improve the solvent resistance of thecured compositions described hereinafter. The epoxidized novolaks(reagent B) are usually preferred by reason of their high solubility inthe solvents ordinarily employed as described hereinafter. Curablecompositions which do not contain component VII are within the scope ofthe invention but are generally not preferred.

The resinous blends contain about 35-60% of component I and about 40-65%of component II. When component VII is present, it comprises an amountup to about 10% of the resinous blend and, in that case, also of thecurable compositions of the invention. All of said percentages are basedon the total resinous components in said blend. The preferredproportions are about 35-45% of component I, about 50-60% of componentII and about 4-8% of component VII. The blends also contain 5-10%,preferably 6-9%, of chemically combined bromine supplied, at least inpart, by component I. The foregoing percentages are exclusive of anysolvent which may be present.

Component III is at least one novolak in which substantially all oxygenis in the form of phenolic hydroxy groups. Thus, it is similar inmolecular structure to the previously described epoxidized novolakexcept that it has not been epoxidized. t-Butylphenol-formaldehydenovolaks are often preferred.

Component IV is at least one compound selected from the group consistingof imidazoles and arylene polyamines. Any of such imidazoles andpolyamines known in the art to be useful as curing agents for epoxyresins may be employed. Particularly useful imidazoles are imidazole,1,2-dimethylimidazole, 2-methylimidazole, 2-heptadecylimidazole and1-(2-cyanoethyl)-2-phenylimidazole. Commercially availableimidazole-arylene polyamine mixtures are often preferred; the especiallypreferred mixtures contain arylene polyamines with a high degree ofalkyl substitution on the aromatic ring, typically at least 3 suchsubstituents. The diethylmethyl-substituted m- and p-phenylenediaminesare generally the most preferred polyamines.

The amount of component IV is selected to achieve rapid cure aftersolvent removal. This requires at least 2 and preferably at least 4.5milliquivalents of basic nitrogen per 100 parts of the curablecomposition, including any basic nitrogen present in the polyphenyleneether (mostly as end groups of formula III). Thus, when a polyphenyleneether essentially free from basic nitrogen is employed the proportion ofcomponent IV must be increased. (For the purpose of this invention, theequivalent weight of an imidazole is equal to its molecular weight andthat of a diamine is half its molecular weight.)

Component V is chemically combined zinc, furnished in the form of a zincsalt which is soluble or stably dispersible in the curable composition.Zinc salts of diketones in which one carbon atom separates the carbonylgroups, especially zinc acetylacetonate, and zinc salts of fatty acids,especially zinc stearate, are examples of suitable forms of zinc forthis purpose. In general, the fatty acid salts are preferred whencomponent IV contains arylene polyamines, and diketone salts arepreferred when component IV is entirely imidazole.

Under certain conditions, zinc bis(acetylacetonate) can form a hydratewhich readily loses acetylacetone and becomes insoluble in the organicsystems used for laminate preparation. Therefore, it may be necessary totake steps to maintain the zinc in stable dispersion.

One means for doing this is to subject the composition to continuousagitation; however, this is generally not practical. A better method isto form an alcoholate of the zinc acetylacetonate, as by reaction withmethanol. Said alcoholate loses alcohol rather than acetylacetone undersimilar conditions, remaining in solution or homogeneous suspension.

Another method for maximizing homogeneity is to employ a zinc fatty acidsalt. Still another method is to employ a titanium compound as acompatibilizer, as disclosed hereinafter.

Component VI is antimony pentoxide, which must also be maintained instable dispersion. This may be done by agitation and/or combination witha suitable dispersing agent, of which many are known in the art.

One preferred dispersing agent is a polymer which is compatible with theresinous constituents of the curable composition but is substantiallynon-reactive under the conditions employed, typically a polyester. Morepowerful dispersing agents, such as amines, may be required whencomponent V is a fatty acid zinc salt, since such salts may otherwiseform insoluble complexes with antimony pentoxide.

The curable compositions of the invention are dissolved in an effectiveamount of an inert organic solvent, typically to a solute content ofabout 30-60%, by weight. The identity of the solvent is not critical,provided it may be removed by suitable means such as evaporation.Aromatic hydrocarbons, especially toluene, are preferred. The order ofblending and dissolution is also not critical. Most often all componentsare initially dissolved therein, but proportions of components andbromine are in terms of components I-V and other resinous materials(including component VII, if present) and brominated materials, and donot include solvent.

In the curable compositions, component III serves as a hardener andcomponent IV as a curing catalyst. Component V has cocatalyticproperties and accelerates curing; it also serves to improve solventresistance and flame retardancy. Component VI functions as a synergistfor the bromine to improve flame retardancy. If it is absent, theproportion of bromine compound required to provide V-0 flame retardancyis much higher, typically about 12%, and the only way to avoidincompatibility of the bromine compound is to use more expensive brominesources.

The broad ranges of proportions of bromine and components I-VII in thecurable compositions of the invention are described hereinabove. Themost preferred proportions are:

    ______________________________________                                        Bromine          6-9%;                                                        Component I      about 30-40%;                                                Component II     about 40-50%;                                                Component III    about 4-8%;                                                  Component IV     about 5-10 milliequivalents                                                   of basic nitrogen;                                           Component V      about 0.1-0.6% of zinc;                                      Component VI     about 1-3% of antimony                                                        pentoxide;                                                   Component VII    about 4.2-4.8%.                                              ______________________________________                                    

Other mateirals may also be present. These include inert, particulatefillers such as talc, clay, mica, silica, alumina and calcium carbonate.In addition, the bromine content of the curable composition may besupplied in part by materials such as alkyl tetraromophthalates and/orepichlorohydrin reaction products with mixtures of bisphenol A andtetrabromobisphenol A. The alkyl tetrabromophthalates also serve asplaticizers and flow improvers. Such materials as antioxidants, thermaland ultraviolet stabilizers, lubricants, anti-static agents, dyes andpigments may also be present.

A material whose presence in minor amount may improve the solventresistance and compatiability of the curable composition, and istherefore preferred, is at least one aliphatictri(dialkylphosphato)titanate. Suitable phosphatotitanates are known inthe art and commercially available. They may be represented by theformula ##STR6## wherein R³ is C₂₋₆ primary or secondary alkyl oralkenyl and preferably alkenyl, R⁴ is C₁₋₃ alkylene and preferablymethylene, R⁵ is C₁₋₅ primary or secondary alkyl, R⁶ is C₅₋₁₂ primary orsecondary alkyl and x is from 0 to about 3 and is preferably 0 or 1.Most preferably, R³ is allyl, R⁵ is ethyl, R⁶ is octyl and x is 0. Thephosphatotitanate is most often present in the amount of about 0.1-1.0part by weight per 100 parts of the resinous composition.

Another aspect of the invention is prepregs comprising a fibroussubstrate (woven or non-woven) such as glass, quartz, polyester,polyamide, polypropylene, cellulose, nylon or acrylic fibers, preferablyglass, impregnated with the curable composition and obtained uponremoval of the solvent therefrom by evaporation or the like. As usedherein, "prepreg" means a curable article comprising a substrateimpregnated with an uncured or partially cured resinous material. Suchprepregs may be cured by application of heat and pressure. The resultingcured articles are other aspects of the invention.

Typically, 2- to 20-ply prepreg laminates are compression molded attemperatures in the range of about 200°-250° C. and under pressures onthe order of 20-60 kg./cm.². Laminates clad with a conductive metal suchas copper, useful for printed circuit board production, may be soprepared and cured by art-recognized methods. As previously mentioned,printed circuit board blanks comprising said laminates are characterizedby excellent dielectric properties, solderability, flame retardancy andresistance to high temperature conditions and solvents. The metalcladding may then be conventionally patterned.

The preparation of the curable compositions, cured compositions andlaminates of this invention is illustrated by the following examples.All parts and percentages are by weight unless otherwise indicated.

In Examples 2-9, the following ingredients were employed:

Component I--the product of Example 1.

Component II--a poly(2,6-dimethyl-1,4-phenylene ether) having a numberaverage molecular weight of about 20,000, an intrinsic viscosity inchloroform at 25° C. of 0.40 dl./g. and a nitrogen content of about 960ppm.

Component III--a commercially available t-butylphenol novolak having anaverage molecular weight in the range of about 700-900.

Component IV:

Imidazole-amine mixture--a mixture of 1,2-dimethylimidazole and isomersof diethylmethylphenylenediamine, having an average equivalent weight ofabout 91.

Component V--zinc acetylacetonate or zinc stearate.

Component VI:

APE 1540--a commercially available colloidal dispersion comprising about40% antimony pentoxide in a polyester resin derived predominantly fromisophthalic acid.

ADP-480--a commercially available colloidal dispersion comprising about75% antimony pentoxide coated with an amine powder and dispersed intoluene.

Component VII--the bisphenol A diglycidyl ether and the "EPN 1138" ofExample 1.

Additional components:

DOTBP--dioctyl tetrabromophthalate.

Brominated epoxy--a product prepared by the reaction of a mixture ofbipshenol A and 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane withepichlorohydrin, containing about 21% bromine.

Phosphatotitanate--a commercially available compound of formula VIIwherein R³ is allyl, R⁴ is methylene, R⁵ is ethyl, R⁶ is octyl and x is0.

EXAMPLES 2-8

A series of curable varnish compositions was prepared by dissolution ofthe ingredients in toluene to a total solids concentration of 35-40%.The compositional data for said varnish compositions are given in TableI. Except for phosphatotitanate and basic nitrogen, all units arepercent by weight.

                                      TABLE I                                     __________________________________________________________________________                    Example                                                                       2   3   4   5   6   7   8                                     __________________________________________________________________________    Component I     29.38                                                                             37.09                                                                             32.31                                                                             27.33                                                                             26.81                                                                             35.65                                                                             36.46                                 Component II    45.70                                                                             37.53                                                                             40.34                                                                             45.55                                                                             44.69                                                                             44.57                                                                             45.58                                 Component III   5.01                                                                              4.26                                                                              8.07                                                                              4.56                                                                              4.47                                                                              8.92                                                                              9.12                                  Component IV:                                                                 2-heptadecylimidazole                                                                         0.87                                                                              0.70                                                                              --  0.73                                                                              0.72                                                                              --  --                                    Imidazole-amine mixture                                                                       --  --  0.56                                                                              --  --  0.62                                                                              0.64                                  Component V:                                                                  Zinc bis(acetylacetonate)                                                                     2.07                                                                              1.71                                                                              1.62                                                                              1.56                                                                              1.53                                                                              --  --                                    Zinc stearate   --  --  1.61                                                                              --  --  1.78                                                                              1.82                                  Component VI:                                                                 APE 1540        7.18                                                                              7.16                                                                              6.94                                                                              --  --  --  --                                    ADP 480         --  --  --  3.97                                                                              3.90                                                                              4.01                                                                              1.82                                  Component VII:                                                                EPN 1138        --  --  4.03                                                                              4.56                                                                              4.47                                                                              4.45                                                                              4.56                                  Bisphenol A diglycidyl ether                                                                  5.44                                                                              7.21                                                                              --  --  --  --  --                                    DOTBP           4.35                                                                              4.34                                                                              4.52                                                                              2.63                                                                              --  --  --                                    Brominated epoxy                                                                              --  --  --  9.11                                                                              --  --  --                                    Phosphatotitanate, parts/100 parts                                            resinous component                                                                            0.50                                                                              0.41                                                                              0.40                                                                              0.47                                                                              0.46                                                                              0.45                                                                              0.46                                  Bromine         6.98                                                                              8.33                                                                              7.57                                                                              7.80                                                                              7.50                                                                              6.26                                                                              6.20                                  Zinc            0.51                                                                              0.42                                                                              0.57                                                                              0.39                                                                              0.38                                                                              0.18                                                                              0.19                                  Antimony pentoxide                                                                            2.9 2.9 2.8 3.0 2.9 3.0 1.37                                  Basic nitrogen, meq./100 parts                                                                5.9 4.9 9.0 5.5 5.4 9.9 10.1                                  __________________________________________________________________________

Swatches of electrical grade woven fiberglass cloth were dipped into thevarnishes of Examples 2-7 and air dried at elevated temperature toremove solvent and yield composite prepregs. Copper-clad laminates werethen prepared from 1-oz. copper foil and 8 plies of the prepregs bycompression molding for 5-10 minutes at 230° C. and 49.2 kg./cm.². Saidlaminates were evaluated for flame retardancy in accordance withUnderwriters Laboratories procedure UL-94. Those prepared from thecompositions of Examples 6 and 7 were also evaluated according tovarious test procedures which form part of military specificationMIL-P-13949. The results are given in Table II.

                                      TABLE II                                    __________________________________________________________________________                         Example                                                                       2  3  4  5  6   7                                        __________________________________________________________________________    Laminat thickness (less copper), mm.                                                               1.42                                                                             1.40                                                                             1.50                                                                             1.56                                                                             1.52                                                                              1.57                                     Resin content, %     -- -- -- -- 37  57                                       UL-94:                                                                        FOT, total sec./5 samples                                                                          25 27 19 27 30  29                                       Rating               V-O                                                                              V-O                                                                              V-O                                                                              V-O                                                                              V-O V-O                                      Water absorption (24 hrs. soak                                                at 23° C.), % -- -- -- -- 0.06                                                                              0.07                                     Flexural strength, MPa.:                                                      Longitudinal         -- -- -- -- 606.7                                                                             --                                       Cross-sectional      -- -- -- -- 379.2                                                                             --                                       Flexural modulus, GPa.:                                                       Longitudinal         -- -- -- -- 22.1                                                                              --                                       Cross-sectional      -- -- -- -- 19.3                                                                              --                                       Izod Impact strength, joules/m.:                                              Longitiudinal        -- -- -- -- NB* --                                       Cross-sectional      -- -- -- -- 671 --                                       Dielectric constant at 1 MHz.:                                                Untreated            -- -- -- -- 4.19                                                                              3.70                                     After 24 hrs. In water at 23° C.                                                            -- -- -- -- 4.24                                                                              3.75                                     Dissipation factor 1 MHz.:                                                    Untreated            -- -- -- -- 0.011                                                                             0.13                                     After 24 hrs. In water at 23° C.                                                            -- -- -- -- 0.012                                                                             0.16                                     Parallel dielectric breakdown                                                 strength, kv.:                                                                Short time                                                                    Untreated            -- -- -- -- 76  --                                       After 48 hrs. In water at 50° C.                                                            -- -- -- -- 78  79                                       Step by step                                                                  Untreated            -- -- -- -- 73  --                                       After 48 hrs. In water 50° C.                                                               -- -- -- -- 64  72                                       Perpendicular dielectric breakdown                                            strength, volts/mil:                                                          Untreated            -- -- -- -- 767 803                                      After 48 hrs. In water at 50° C.                                                            -- -- -- -- 783 --                                       Peel strength, kg./cm.                                                                             -- -- -- -- >1.4                                                                              >1.4                                     Methylene chloride resistance, % absorbed                                                          -- -- -- -- 0   1.44                                     __________________________________________________________________________     *No break.                                                               

EXAMPLE 9

A 75% solution in toluene of the upstaged composition of Example 1 wasprepared and 640 parts thereof (component I) was combined with 2252parts of hot toluene, 600 parts of component II, 120 parts of componentIII, 10.2 parts of 2-heptadecylimidazole (component IV), 24 parts ofzinc acetylacetonate (component V), 42 parts of ADP-480 (component VI),60 parts of "EPN 1138" (component VII) and 6 parts of phosphatotitanate,to prepare a curable varnish containing 7.5% bromine, 0.45% zinc, 2.4%antimony pentoxide and 5.5 milliequivalents of basic nitrogen per 100parts. Swatches of electrical grade woven fiberglass cloth were dippedinto said varnish and air dried at elevated temperature to removesolvent and yield composite prepregs. Copper-clad laminates were thenprepared from 10 plies of the prepregs by compression molding for 10minutes at 240° C. and 28.1 kg./cm.².

The laminates were subjected to physical testing in comparison with thefollowing controls, based on the disclosure of Japanese Kokai No.58/69052:

Control A--identical to Example 9 except that an upstaged compositionprepared from 66.7 parts of bisphenol A diglycidyl ether and 33.3 partsof 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane was employed and thephosphatotitanate was omitted.

Control B--a curable composition was prepared from 600 parts ofpolyphenylene ether, 400 parts of bisphenol A diglycidyl ether, 73 partsof m-phenylenediamine, 1 part of triethylamine hydrochloride and 2252parts of toluene; a 10-ply laminate was molded at 200° C. and 28.1kg./cm.² for one hour. The procedure was essentially that of Example 2of the Japanese Kokai.

The test results are given in Table III.

                  TABLE III                                                       ______________________________________                                                      Invention                                                                            Control A Control B                                      ______________________________________                                        Glass transition                                                                              221      220       190                                        temperature, °C.                                                       Methylene chloride                                                                            0        10        0                                          resistance, % absorbed                                                        Appearance after methylene                                                                    Good     Severe    Severe                                     chloride immersion       erosion   whitening                                  Z-axis expansion, %                                                                           1.3      4.1       3.4                                        ______________________________________                                    

It is apparent that the phosphatotitanate-containing compositions ofthis invention afford laminates with properties superior to those oflaminates prepared according to the Japanese Kokai.

What is claimed is:
 1. A curable composition containing chemicallycombined bromine in an amount effective to impart flame retardancy andcomprising:(I) about 25-50% of a resinous composition containing 15-20%chemically combined bromine and comprising the reaction product obtainedby heating at a temperature in the range of about 125°-225° C., in thepresence of a catalytic amount of at least one basic reagent, a mixturecomprising: (A) at least one halogen-free bisphenol polyglycidyl etherhaving an average of at most one aliphatic hydroxy group per molecule;(B) about 15-25% of at least one halogen-free epoxidized novolak; and(C) 25-35% of at least one bisphenol containing bromine as arylsubstituents; the percentages of components B and C being based on totalreagents A, B and C; (II) about 35-55% of at least one polyphenyleneether; (III) about 4-15% of at least one halogen-free noyolak,substantially all oxygen therein being in the form of phenolic hydroxygroups; (IV) an amount of at least one of imidazoles and arylenepolyamines to provide a total of at least 2 milliequivalents of basicnitrogen per 100 parts of said curable composition; (V) about 0.1-1.0%of zinc in the form of a zinc salt which is soluble or stablydispersible in said curable composition; and (VI) about 1-4% of antimonypentoxide stably dispersed in said curable composition; said compositionbeing dissolved in an effective amount of an inert organic solvent; saidpercentages being by weight and based on the total of components I-VIand any other resinous materials and brominated materials present.
 2. Acurable composition containing chemically combined bromine in an amounteffective to impart flame retardancy and comprising:(I) about 25-50% ofa resinous composition containing 15-20% chemically combined bromine andcomprising the reaction product obtained by heating at a temperature inthe range of about 125°-225° C., in the presence of a catalytic amountof at least one basic reagent, a mixture consisting essentially of: (A)at least one halogen-free bisphenol polyglycidyl ether having an averageof at most one aliphatic hydroxy group per molecule; (B) about 15-25% ofat least one halogen-free epoxidized novolak; and (C) 25-35% of at leastone bisphenol containing bromine as aryl substituents; the percentagesof components B and C being based on total reagents A, B and C; (II)about 35-55% of at least one polyphenylene ether; (III) about 4-15% ofat least one halogen-free novolak, substantially all oxygen thereinbeing in the form of phenolic hydroxy groups; (IV) an amount of at leastone of imidazoles and arylene polyamines to provide a total of at least2 milliequivalents of basic nitrogen per 100 parts of said curablecomposition; (V) about 0.1-1.0% of zinc in the form of a zinc salt whichis soluble or stably dispersible in said curable composition; and (VI)about 1-4% of antimony pentoxide stably dispersed in said curablecomposition; said composition being dissolved in an effective amount ofan inert organic solvent; said percentages being by weight and based onthe total of components I-VI and any other resinous materials andbrominated materials present.
 3. A composition according to claim 2wherein reagent A has the formula ##STR7## wherein n has an averagevalue up to 1; reagent B is a novolak prepared from formaldehyde, phenoland epichlorohydrin and reagent C is2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; said composition alsocontaining (VII) an amount up to about 10% of at least one polyepoxycompound selected from halogen-free bisphenol polyglycidyl ethers havingan average of at most one aliphatic hydroxy group per molecule andhalogen-free epoxidized novolaks.
 4. A composition according to claim 3wherein n is 0, component II is a poly(2,6-dimethyl-1,4-phenylene ether)having a number average molecular weight within the range of about12,000-40,000 and component VII is an epoxidized novolak and is presentin the amount of about 4-8%.
 5. A composition according to claim 4wherein the solvent is toluene.
 6. A composition according to claim 4wherein component VII is prepared from phenol, formaldehyde andepichlorohydrin.
 7. A composition according to claim 4 wherein componentIV is at least one imidazole and provides a total of at least 4.5milliequivalents of basic nitrogen per 100 parts of said curablecomposition.
 8. A composition according to claim 4 wherein component IVis a mixture of at least one imidazole with at least one arylenepolyamine and provides a total of at least 4.5 milliequivalents of basicnitrogen per 100 parts of said curable composition.
 9. A compositionaccording to claim 4 wherein component V is zinc acetylacetonate or zincstearate.
 10. A composition according to claim 9 wherein the proportionsare:

    ______________________________________                                        Bromine          6-9%;                                                        Component I      about 30-40%;                                                Component II     about 40-50%;                                                Component III    about 4-8%;                                                  Component IV     about 5-10 milliequivalents                                                   of basic nitrogen;                                           Component V      about 0.1-0.6% of zinc;                                      Component VI     about 1-3% of antimony                                                        pentoxide;                                                   Component VII    about 4.2-4.8%.                                              ______________________________________                                    


11. A composition according to claim 10 wherein the polyphenylene ethercomprises molecules having end groups of the formula ##STR8## whereineach R² is independently hydrogen or a C₁₋₆ primary alkyl radical.
 12. Acomposition according to claim 11 wherein each R² is n-butyl.
 13. Acomposition according to claim 4 which also contains at least onealiphatic tris(dialkylphosphato)titanate of the formula ##STR9## whereinR³ is C₂₋₆ or secondary alkyl or alkenyl, R⁴ is C₁₋₃ alkylene, R⁵ isC₁₋₅ primary or secondary alkyl, R⁶ is C₅₋₁₂ primary or secondary alkyland x is from 0 to about 3, in the amount of about 0.1-1.0 part byweight per 100 parts of the resinous composition.
 14. A compositionaccording to claim 13 wherein R³ is alkyl, R⁴ is methylene, R⁵ is ethyl,R⁶ is octyl and x is 0 or
 1. 15. A curable composition containingchemically combined bromine in an amount effective to impart flameretardancy and comprising:(I) about 25-50% of a resinous compositioncontaining 15-20% chemically combined bromine and comprising the productobtained by the reaction, in the presence of a catalytic amount of atleast one basic reagent, of: (A) at least one halogen-free bisphenolpolyglycidyl ether having an average of at most one aliphatic hydroxygroup per molecule; (B) about 15-25% of at least one halogen-freeepoxidized novolak; and (C) 25-35% of at least one bisphenol containingbromine as aryl substituents; the percentages of components B and Cbeing based on total reagents A, B and C; (II) about 35-55% of at leastone polyphenylene ether; (III) about 4-15% of at least one halogen-freenovolak, substantially all oxygen therein being in the form of phenolichydroxy groups; (IV) an amount of at least one of imidazoles and arylenepolyamines to provide a total of at least 2 milliequivalents of basicnitrogen per 100 parts of said curable composition; (V) about 0.1-1.0%of zinc in the form of a zinc salt which is soluble or stablydispersible in said curable composition; and (VI) about 1-4% of antimonypentoxide stably dispersed in said curable composition; said compositionbeing dissolved in an effective amount of an inert organic solvent; saidpercentages being by weight and based on the total of components I-VIand any other resinous materials and brominated materials present.
 16. Acomposition according to claim 15 which also contains (VII) an amount upto about 10% of at least one polyepoxy compound selected fromhalogen-free bisphenol polyglycidyl ethers having an average of at mostone aliphatic hydroxy group per molecule and halogen-free epoxidizednovolaks.
 17. A composition according to claim 16 which also contains atleast one aliphatic tris(dialkylphosphato)titanate of the formula##STR10## wherein R³ is C₂₋₆ primary or secondary alkyl or alkenyl, R⁴is C₁₋₃ alkylene, R⁵ is C₁₋₅ primary or secondary alkyl, R⁶ is C₅₋₁₂primary or secondary alkyl and x is from 0 to about 3, in the amount ofabout 0.1-1.0 part by weight per 100 parts of the resinous composition.